The present invention relates to the field of fixed abrasive substrates. More particularly, the invention relates to a method and apparatus for fixed abrasive preparation and use in a cluster chemical-mechanical polishing (CMP) tool.
One of the last stages before fabrication of semiconductor devices on a semiconductor substrate, such as Si or III-V related compounds (e.g. GaAs, InP), involves the polishing of the semiconductor wafer. One reason wafer polishing is performed is to remove any irregularities present on the surface so that the wafer is smooth and flat prior to performing any initial fabrication steps (such as etch, metalization or photolithography). In addition, CMP is also used to planarize the semiconductor wafer subsequent to initiation of device fabrication, for example after deposition of polyamide or other insulating material on the wafer.
In general, prior to device fabrication, there are two types of polishing: rough polishing and chemical-mechanical polishing (CMP) in which the rough polishing precedes the CMP. Rough polishing is a conventional abrasive process whose primary purpose is to remove the surface damage leftover from the wafer-slicing process of diamond saws that created the wafer. CMP follows the rough polishing and is typically a combination of chemical etching and mechanical buffing. During device fabrication, only CMP is used as rough polishing is too abrasive to afford the necessary planarization control.
In a conventional CMP rotary or orbital system, wafers are mounted upside-down on rotating circular holders and lowered onto a polishing pad rotated in the opposite direction. The polishing pad is generally polyurethane or urethane-coated with felt and sits on a pallet. For ridding the surface of irregularities prior to fabrication, a slurry containing silica suspended in a mild etchant such as potassium or ammonium hydroxide is added to the polishing pad. A thin layer of silicon dioxide chemically grows on the surface of the wafer as a result of contact with the alkaline slurry. This layer is continuously removed mechanically by the buffing action of the polishing pad. The process generally reduces the irregularities of the wafer to a small percentage of the wafer diameter over the entire surface of the wafer. For planarization during processing, e.g. planarizing to flatten the wafer profile in multi-metal interconnection schemes, the CMP apparatus must remove oxides and various metals in addition to any planarizing material and/or wafer material.
To achieve the necessary precision without polishing away the active circuitry, a number of variables in any CMP apparatus can be controlled. For example, the numerous diverse variables that can be controlled include: composition of the slurry, rate of feed or introduction of the slurry to the pad, pad characteristics (both the pad material and the condition of the pad), polishing time, rotational speed of both the pad and wafer, and pressure of the wafer on the pad. The slurry characteristics to be controlled include the particulate size and pH of the etchant solution. In addition, slurries are chosen to balance chemical removal with abrasiveness so that the production rate of wafers through the CMP apparatus is acceptable (as is the planarity of the resultant wafer).
More recently, some current CMP systems/modules have eschewed conventional slurries as described above, turning to fixed abrasive polishing instead. To date, a number of forms of fixed abrasives exist. Materials are produced either as a roll or as a fixed pad. The roll is slowly and continuously fed into a CMP module, while the fixed pad is applied to the conventional rotary or orbital system. At least one of the problems with these current fixed-abrasive CMP systems is similar to that of more-conventional slurry-type systems; a high cost of ownership of the system for the user. Additional problems include both inconsistent results of the fixed abrasive as the abrasive wears away due to usage and reliance on third-party produced consumable abrasive or slurry material.
To solve these problems, an arrangement containing a modified fixed abrasive material and method of using the same has been developed using a pre-patterned substrate onto which the fixed abrasive is disposed.
A first aspect of the present invention is directed towards a method of fixed abrasive substitute preparation and use. The method entails providing a substrate having a predetermined pattern on a surface of the substrate and introducing an abrasive/binder mixture to the surface of the substrate. The abrasive/binder mixture coats the pattern on the surface of the substrate. A semiconductor wafer is planarized to a desired uniformity by the interaction of coated substrate and the semiconductor wafer. In one embodiment, the method may include patterning the substrate prior to introducing the abrasive/binder mixture to the surface of the substrate. Introducing the abrasive/binder mixture to the surface of the substrate may include vacuum depositing the abrasive/binder mixture o n the surface of the substrate. Similarly, the method may include a cure mechanism enabling curing of the binder such that the abrasive better adheres to the surface of the semiconductor. In other embodiments, the method may include stripping the substrate of remaining abrasive subsequent to planarizing semiconductors wafers. The stripping of the abrasive occurs in cleaning chamber and the substrate would be subsequently transferred to a deposition chamber in which the substrate would be re-coated with the abrasive/binder mixture to which new semiconductor wafers requiring planarization may be applied.
A second aspect of the present invention is directed towards an arrangement using a pre-patterned substrate containing a fixed abrasive coated on a surface of the substrate and a wafer to which the coated substrate is applied. The second aspect of the invention may also include a vacuum deposition chamber in which an abrasive/binder mixture is applied and a chemical-mechanical polishing chamber to which the substrate and wafers are introduced and the wafer planarized. A curing mechanism may also be included in which the abrasive/binder mixture is annealed, allowing the abrasive to better adhere to the surface of the substrate. The second aspect of the invention may also incorporate the use of a cleaning chamber in which the remaining abrasive after planarization is stripped from the surface of the substrate and after which the substrate is transferred to the deposition chamber and the abrasive/binder mixture is reapplied to the surface of the substrate.
It is therefore an advantage of the present invention to increase the reliability and decrease the cost of a CMP system by providing an arrangement and method to better control the amount of abrasive material used during planarization of a semiconductor wafer. An additional advantage of the present invention is the improvement in process control of the planarization of the semiconductor wafer.
The following figures and detailed description of the preferred embodiments will more clearly demonstrate these and other objects and advantages of the invention.